Question: Christopher works out for $\frac{5}{6}$ of an hour every day. To keep his exercise routines interesting, he includes different types of exercises, such as sit-ups and jumping jacks, in each workout. If each type of exercise takes $\frac{5}{18}$ of an hour, how many different types of exercise can Christopher do in each workout?
To find out how many types of exercise Christopher could do in each workout, divide the total amount of exercise time ( $\frac{5}{6}$ of an hour) by the amount of time each exercise type takes ( $\frac{5}{18}$ of an hour). $ \dfrac{{\dfrac{5}{6} \text{ hour}}} {{\dfrac{5}{18} \text{ hour per exercise}}} = {\text{ number of exercises}} $ Dividing by a fraction is the same as multiplying by the reciprocal. The reciprocal of ${\dfrac{5}{18} \text{ hour per exercise}}$ is ${\dfrac{18}{5} \text{ exercises per hour}}$ $ {\dfrac{5}{6}\text{ hour}} \times {\dfrac{18}{5} \text{ exercises per hour}} = {\text{ number of exercises}} $ $ \dfrac{{5} \cdot {18}} {{6} \cdot {5}} = {\text{ number of exercises}} $ Reduce terms with common factors by dividing the $5$ in the numerator and the $5$ in the denominator by $5$ $ \dfrac{{\cancel{5}^{1}} \cdot {18}} {{6} \cdot {\cancel{5}^{1}}} = {\text{ number of exercises}} $ Reduce terms with common factors by dividing the $18$ in the numerator and the $6$ in the denominator by $6$ $ \dfrac{{1} \cdot {\cancel{18}^{3}}} {{\cancel{6}^{1}} \cdot {1}} = {\text{ number of exercises}} $ Simplify: $ \dfrac{{1} \cdot {3}} {{1} \cdot {1}} = {3} $ Christopher can do 3 different types of exercise per workout.